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Date Created: 03/06/16
PHYS 104: Astronomy Week 3 Course Notes, 2/15 – 2/19 Definitions Orbital Period: The amount of time required to complete one orbit. Orbital Velocity: The speed of the planet in orbit. Emperical: Not based on an assumption on how the universe works. Inertia: Amassive object's tendency to resist change. Force: Apush or pull resulting in the movement of an object and acceleration. Position: Where an object is with respect to some reference. Velocity: The rate in which the position is changing. Acceleration: The rate in which the velocity is changing. Aristotle • According to Aristotle, each celestial object is embedded in a crystal sphere. • Each sphere rotates around Earth at a fixed rate. This wasn't able to explain retrograde motion. Ptolomy • Created the first model including epicycles Heliocentric model with epicycles Nicholas Copernicus • Created the first heliocentric model ◦ A simple solution to the retrograde motion of planets ◦ Has simple orbital period calculations ◦ This model was no more accurate than Ptolomey's Tycho Brahe • Took 2 decades worth of naked eye planet observations. • His new model had accuracy to within one minute arc. Johannes Kepler • A student of Tycho, who studied his data. • Discovered three empirical relationships. • Trusted Copernicus' model. • Suggested that the sun exerts a force on the planets. nd 2 Law:A line joining a planet and the sun sweeps out equal areas during equal intervals of time. (Fast at perihelion, slow at aphelion.) Distance traveled = Velocity x Time 3 Law: P²=a³ where P is the orbital period and a is the semi-major axis. Isaac Newton • Three laws of motion • Universal Gravitation • Calculus Simple central principles from which all motion can be derived. 1 Law: Left on their own, massive bodies have a constant velocity. nd 2rdaw: Forces cause a change in velocity. F=ma 3 Law: If you apply a force to something, it pushes back. Universal Law of Gravitation: Objects with mass exert an attractive force on one another. PHYS 104: Astronomy Week 4 Course Notes, 2/22 – 2/26 Definitions Momentum: Mass of an object times the velocity. mv Kinetic Energy: Energy of an object with respect to its motion. Potential Energy: Energy of an object with respect to position or arrangement of a system. Radiative Energy: Energy transmitted through particles by waves. III. Conservation Laws A. Momentum P=mv 1. In a closed system, momentum is always conserved. a. This means that the amount of momentum will never change from the beginning of an event within a give system to the end. b. This includes systems where a gravitational force is involved. c. This also includes systems where energy is transferred. d. This only holds as long as there are no external forces on the system. B. Angular Momentum l=mvr 1. Closed systems also conserve angular momentum. 2. Angular momentum takes into account the distance of a massive object from its pivot point. IV. Energy A. All forms of energy fit into one or more of three types of energy: 1. Kinetic Energy K=(1/2)mv^2 a. Motion (for example) 2. Radiative Energy a. Light 3. Potential Energy a. Gravitational b. Chemical c. Springs / rubber bands d. Potential energy can be converted into either Kinetic or Radiative Energy. B. Mass Energy E=mc^2 1. Is a form of potential energy. 2. The total energy is the mass times the speed of light squared. C. Energy is conserved
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